Diamond possesses many desirable physical properties such as hardness, chemical inertness, infrared transparency, and excellent heat conductivity coupled with very high electrical resistivity. Consequently, diamond is a material with many important technological applications such as in optical devices, semiconductors, heat sinks, abrasives, tool coating etc. It can also be used as a high-grade, radiation resistant, high-temperature semiconductor with potential application in many military and aerospace technologies. There is considerable incentice to find practical ways to synthesize diamond for these many and varied applications.
A prior art thermal dissociation low pressure chemical vapor deposition (LPCVD) system is shown in FIG. 1. It consists essentially of a quartz tube 10 typically a few inches in diameter and 8 inches high enclosed at each end by suitable end pieces 12. The diamonds are synthesized from a dilute mixture of a hydrocarbon gas (typically methane) and hydrogen. The hydrocarbon content is usually varied from 0.1 to 2.5% of the total volumetric flow. The gas is introduced via a quartz tube 14 located just above a hot tungsten filament 16 which is electrically heated to between 1750.degree.-2150.degree. C. The gas dissociates at the filament surface, and diamonds are condensed onto a heated substrate 18. The substrate is held in a resistance heated molybdenum boat 20 and heated to temperatures in the region of 700.degree.-1100.degree. C.
Additionally, plasma discharge has been used in conjunction with the basic system described above. The plasma discharge serves to increase the nucleation density, growth rate, and it is believed, to enhance formation of diamond films as opposed to discrete particles. The formation of diamond films is important in many applications such as for use as semiconductor materials. Of the plasma systems that have been utilized in this area, there are only three basic systems. One is a microwave plasma system, the second is an RF (inductively or capacitively coupled) plasma system and the third is a D.C. plasma system. The RF and the microwave plasma systems utilize relatively complex and expensive equipment which usually requires complex tuning or matching networks to electrically couple electrical energy to the generated plasma. Additionally, the diamond growth rate offered by these two systems is quite modest, about 1 micron per hour.
What is needed is a diamond synthesis system capable of very high growth rates over large areas which is relatively simple in structure and operation, and which includes the advantageous characteristics of both thermal LPCVD and plasma LPCVD systems.